In recent years, a device of detecting spatial information such as the presence of an object in a target space, or the outline and shape of the object by irradiating a light into the target space, and receiving a reflection light from the target space has been practically utilized in various technical fields of, for example, realizing quality control in factory automation, security system at airport and station, and an TV interphone system for household use.
For example, Japanese Patent Early Publication [kokai] No. 2001-148808 discloses a solid-state image pickup device, which has the capability of providing a clear image of an object by removing the influence of environmental light. This solid-state image pickup device has two CCDs for storing electric charges with respect to one photodiode. Electric charges received in a lighting period and a non-lighting period of a light emitting portion are stored in the respective CCDS, and then a difference signal therebetween is used to cancel the influence of environmental light.
In addition, International Publication No. 2004/090994 discloses a spatial information detecting device having an excellent S/N ratio and an increased aperture ratio. This spatial information detecting device is provided with a photoelectric converter for generating amounts of electric charges corresponding to an intensity of received light, a charge collection region formed in the photoelectric converter by applying a control voltage to an electrode on the photoelectric converter to collect the electric charges generated in the photoelectric converter, a charge ejecting portion for outputting the electric charges from the charge collection region, and a sensitivity controller for controlling the control voltage to change the size of the charge collection region.
However, the conventional devices described above still have plenty of room for improvement from the viewpoints of improving the detection efficiency of the spatial information, developing a method of effectively evaluating the detected information, improving the operation stability of the detecting device under special circumstances that the received light output is saturated, and simplifying the complex structure of the conventional detecting device, in addition to removing the influence of environmental light.